No hang when inserting a list over uneditable element in contenteditable
While firstEditablePositionAfterPositionInRootAlgorithm() is running,
we can get the next editable paragraph under the highest editable
node by skipping non-editable paragraph.
However, if an editable paragraph has a non-editable child, the next
paragraph can be the same editable paragraph that is the parent of the
non-editable child. In this case, we can't get the next editable
paragraph in InsertListCommand::doApply's while loop. As a result,
the while loop can't break, which makes the tab hang.
Here is the example:
This CL allows to get the next editable paragraph by considering the
non-editable child element.